eeweb pulse - issue 57, 2012

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TABLE OF C ONTENTS

Rod Callison 4RAYTHEON MISSILE SYSTEMS

Featured Products 10

Pulling Energy Out of Thin AirBY OLIVER SCZESNY WITH ENOCEAN

Improved Noise Figure Using an FDA

and Input TransformerBY MICHAEL STEFFES WITH INTERSIL

RTZ - Return to Zero Comic 22

With energy harvesting becoming a popular power solution, more companies are looking attheir surroundings for energy potential.

Interview with Rod Callison - Engineering Fellow

Deliver high gains with improved signal-to-noise ratio using an input transofrmer into a differntialinverting amplifier design.

12

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4/22



INTERVIEW

and execution of the simulation.

We could pick up the fan-folded

printouts a couple of hours after job

submittal. This was a big upgrade

to the punched cards engineers hadbeen using just a couple of years

before.

The engineers at

Raytheon are brilliant

and they are always

willing to take the

time to help someone

learn, whether that

someone is a new-hire

or an old dog like me.

After two years, I wanted to do

more design and transferred to the

RF Guidance department. We

werent so specialized back then

and I had the chance to do digital,

analog, and software design. Over

the years the defense industry grew,

declined, and grew again; divisions

of GD split and merged; GDs

missile business was purchased

by Hughes Aircraft who moved toTucson before being purchased by

Raytheon. Departments evolved

into more specialized disciplines

and I am currently in the RF

Subsystems department where I

do primarily RF analysis.

What were some of yourprevious positions at Raytheonand the projects you workedon?

Ive pretty much always been justan engineer. Ive been the team

lead on a number of projects, the

principal investigator on a number

of IRADs, and am currently the

functional manager for the senior

members of my department. But,

so far, I have successfully avoided

any promotion that would take me

too far from the technical.

One of my first projects started

as an IRAD, for which I was

Principal Investigator, and ended

as a contract, for which I was

the RF team lead. Stinger is a

lightweight fire-and-forget short-

range air defense missile equipped

with an advanced passive two-color

infrared/ultraviolet (IR/UV) detector.

We added a passive, two-port,

rolling interferometric RF sensor

and changed its role to air-to-ground

to suppress enemy air defenses bya scout helicopter. I was able to

spend one summer flying around

the Redstone Arsenal in a UH-1H

helicopter during flight tests.

Ive also worked digital design for

the guidance computer on Standard

Missile, a semi-active radar

system, and provided analysis for

AMRAAM, an active radar.

What have been some of yourinfuences that have helpedyou get to where you aretoday?

That would have to be the people

with whom Ive had the privilege to

work. The engineers at Raytheon are

brilliant, and they are always willing

to take the time to help someone

learn, whether that someone is anew-hire or an old dog like me.

Do you have any tricks upyour sleeve?

If I could offer one piece of advice,

it would be to focus on the basics. I

taught electronics engineering part-

time at Cal Poly, Pomona, early in

my career, which forced me to have

a very solid understanding of the

basic principles of digital designand analysis. This, in turn, gave

me insights into the more complex

problems I was encountering at

work. Time and time again Ive

Stinger



INTERVIEW

seen engineers skip a fundamental

understanding of the system in

their impatience to get to the final

solution, which seems to elude

them.

What has been your favoriteproject?

The one that first comes to mind was

a fairly short task I did several years

ago. It was to write an FFT function

for the ESSM rear receiver.

Processing time was critical, so

it would have to be optimized for

speed and written in assembly

language on a processor wed never

used before, with a development

system wed never used before.

Requirements were challenging,

and the schedule even more so.

The program manager needed to

know if the processing timelinecould be met, and he needed to

know by the end of the year. I was

working another program and had

limited spare time. The PM told

me that I was one of two engineers

at RMS that could do the job, and

the other person was already fully

engaged. Of course he had me

hooked at that, whether it was true or

not. I fleshed out the requirements;

developed, optimized, and tested

and timed the code; and delivered

a finished product by year end. To

my knowledge, that code has never

needed modification.

Will you tell us about the twopatents related to radar missile

guidance that you hold? Aswell as being member of thePatent Committee?

My first patent was the Multi-

dimensional in-line linearization

PROM. I was tasked to design

a circuit that would linearize

commands to an AGC amplifier.

The obvious solution was to map

the linearization in a PROM, but the

only PROMs I could find had many

times the memory capacity than Ineeded. I hate wasting anything, so

I found a use for the extra memory.

The program manager liked the

idea and asked me to pursue a

patent. I thought it was just good

engineering, but I did as I was told

and to my great surprise a patent

was issued. My second patent was

an FPGA implementation of the

Polar Format Algorithm for Synthetic

Aperture Radar. I was working on

a project that required such an

implementation and asked a fellow

engineer, for whom I have the

greatest respect and had expertise

in that area, if he knew of such a

design. Not only was he unaware

of any such design, but he had

seriously doubts that it could even

be done. Nothing he could have

said would have been a greater

motivator. I made it my mission to

prove him wrong. And I did.

Some of myrecent career

highlights includemy promotion to

Engineering Fellow,

having two patentsissued as the sole

inventor, and havingthe opportunity toserve on the RMSPatent Committee.

Three years ago, I had the

opportunity to become a member

of the Patent Committee at RMS,

or as it is more officially know, the

Invention Review Committee. This

has been a tremendous learning

experience. I am in awe of the talent

we have at RMS and the innovation

Stinger



INTERVIEW

that is taking place in all aspects of

engineering.

What are you currentlyworking on?

I support a number of programs,

but one of the more interesting

things Im working on is a paper

describing a class of biphase codes

used in radar pulse compression.

Much work has been done in the

past on biphase codes, but this niche

seems to have been overlooked.

Ive written a C program to search

for the codes and Matlab scripts to

analyze expected performance and

characteristics. Its been fun andeducational, and I hope to get the

paper published some day.

Can you tell us more aboutRaytheon and the technologythey are developing?

Raytheon Missile Systems is

located in Tucson, Arizona, though

there are satellite facilities in

Kentucky, New Mexico, Arkansas,

Alabama, and California. RMSis a premier designer, developer

and producer of tactical weapons

systems for the United Stated and

many allied nations, For more than

60 years,RMS products have been

deployed by the U.S. military, and

the armies, navies and air forces of

more than 40 countries. RMS has

developed and supports a broad

range of cutting-edge weapons that

includes missiles, smart munitions,projectiles, kinetic kill vehicles,

space vehicles and directed energy

effectors. RMS employs nearly

12,000 people and had $5.6B in

revenue last year. Technology being

developed includes advanced

designs in active, passive, and semi-

active radar and signal processing

for missile guidance; directed-

energy, non-lethal weapons;

advanced electro-optical seekers;

and automated factory test facilities.

How does Raytheon continueto be a leading producer ofmissile systems for U.S. andallied forces, including air-to-air, strike, naval weaponsystems, land combat?

I believe that Raytheon has a

reputation for producing some of

the worlds most technologically

advanced and capable weapons.

RMS products are meeting todays

threats and we are continuallyevoling to support the future

battlespace and its ever-changing

threats. We work closely with our

customers to understand their

needs so we can develop innovative

products and solutions that fulfill

our customers needs. RMS has

a focus on quality, cost, and on-

time delivery. Were committed to

providing systems that customers

can rely on to perform as neededevery time. This promise of Mission

Assurance has been proven

continually in critical missions and

has kept us a leader in the field.

What is the work culture like atRaytheon?

Raytheon Missile Systems is a blend

of cultures from the companies

that merged in the 1990s to

form it: Hughes Aircraft, General

Dynamics, Texas Instruments, E

Systems, and of course Raytheon.

This has given us the opportunity

to select the best of each culture

to create the environment we

have today. Engineers are given

a lot of opportunities to shape

their careers into what they want

them to be. Raytheon Missile

Systems engineers fully realize

the importance of helping tofoster student interest in math and

science. One of the things that RMS

Engineers have the opportunity to

do is volunteer and visit schools and

speak in classrooms year around to

help support future generations in

science, technology, and math.

What are some newtechnologies we can expect

to see from Raytheon MissileSystems in the near future?

I wish I could tell you. I really do.

But the coolest technologies being

developed are held as company

Rod Callison - Engineering Fellow



INTERVIEW

proprietary and competition

sensitive. Stay tuned and watch for

public releases.

Raytheon is well positioned as a

global leader in technology anddefense. We have a wide portfolio

products and we continue to exceed

our customers expectations in all

of the domains we serve. We will

pursue adjacent markets such as

foreign sales and partnerships,

and commercial sales. Cost, as a

design driver, will be given much

more weight. There will be an even

greater emphasis to delivering on

schedule and within budget. Wewill continue on with our history of

innovation that spans more than 90

years.

What challenges do youforesee in our industry?

The biggest challenge to the

defense industry is a shrinking

budget for development work. We

need to deliver products with the

capabilities the warfighter needs at

a cost the government can afford.

We cannot cut corners to sacrifice

quality or reliability because lives

literally depend on our products

working as advertised. I believe

that at RMS we have the talent to

find innovative solutions to these

challenges. And engineers love a

challenge, right?

What are some of yourhobbies outside of work anddesign?

Ive spent a week backpackingin Californias Sierra Nevada

Mountains nearly every summer

for the last 30 years, and hope

to continue many more years. I

love the feeling of independence,

carrying everything I need in my

pack, and seeing mountains and

valleys that can be seen no other

way. My wife and I also enjoy

traveling and have been fortunate

to go on some pretty exciting trips:

weve visited the landing beaches in

Normandy, hiked in the Swiss Alps,

cruised the Mediterranean, walked

the Great Wall of China, spent the

night in a Buddhist monastery in

Japan, watched a solar eclipse in

Turkey, explored Inca ruins in Peru,

and camped on the savannas in

Zambia.

Is there anything that youhave not accomplished yet,that you have your sights on

accomplishing in the nearfuture?

In the very near future, my wife and

I plan to track mountain gorillas in

Uganda. And there are still many

other places in the world wed like

to visit.
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9/22

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FEATURED PRODU CTS

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This highly functional, multipurpose DC to DC converter delivers 54

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of 2250 VDC. The module conforms to the Industry Standard, DOSA

half-brick package measuring 58.4 61 12.7 mm (2.3 2.4 0.5

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For more information, please click here.

Torque Sensor Transducers with Integral Electronics

The new TorqSense RWT410/420 torque sensors, which replace the

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RF Multi-Measurement Signal Analyzer

Vishay Intertechnology, Inc. introduced the industrys first remote control

code learning IC to integrate signal detection and processing into onecomponent. Optimized for universal remote controllers, the VSOP98260

simplifies the code learning process by amplifying and shaping the

signal received by the infrared emitter already present in these devices.

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8M Fast CMOS SRAMs in 44-Pin

Alliance Memory is adding to its extensive line of legacy high-speedCMOS SRAMs with two new 8M ICs in the 44-pin, 4-mil TSOP-II and

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11/22

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Dave Baarman

DirectorOfAdvanced Technologies

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TECHNICAL ARTICLE

Out of

Thin Air

PullingEnergy

Oliver SczesnyEnocean, Inc. - ApplicationEngineering Manager, Co-founder

Hardwired line power has been available in buildings for

more than a century. The original two-pin electrical plug

and socket was invented and patented in 1904. Nowthat we are fully immersed in the digital age, we have

become more dependent upon energy than ever. Due

to the steady increase in energy costs and its converse

diminishing supply; innovators have stepped up to

create solutions that reduce energy costs and unwanted

energy by-products such as CO2 emissions. Buildings

have proved a rich habitat for innovation.

Since buildings account for more than 40 percent of the

energy consumption in the US, OEMs can capitalize

on the shared need for more energy-efficient buildings.

Energy harvesting serves as a great example of onesuch innovation.. Energy harvesting allows sensor

networks to operate independently of an external power

supply. This is accomplished by harvesting energy

from our surroundings (i.e., from motion, indoor light

or differences in temperature). Ten years ago, energy

harvesting was a term only known to a small group of

specialists; but now there is a diverse range of wireless

products on the market that are powered by energy

harvesting technology.

The EnOcean wireless standard, a pacesetter in the field

and a catalyst to the development of energy autonomous

wireless solutions, serves a host of applications inbuilding automation. In 2012, the open EnOcean

protocol was ratified by the International Electrotechnical

Commission (IEC) as an international standard (ISO/

IEC 14543-3-10).

The Evolution of Power in Buildings

In addition to line and battery power, alternative power

sources exist. The last decade has yielded a new

generation of energy-autonomous solutions that eliminate

the need for wires and batteries as power sources.

Energy harvesting technology enables engineers tothink beyond the constraints imposed by traditional

power sources.

Negative impacts of Line Power

Particularly in building retrofits, cables are difficult to

run to the locations where energy management controls

are needed.

Line power is made of irreplaceable natural resources



TECHNICAL ARTICLE

such as copper, which is sharply increasing in price.

Negative Impacts of Battery Power

High maintenance Battery life is typically 6 months to2 years. This means that if the product is designed to last

more than 20 years, then the building owner will have to

pay for the upkeep of each device 10 40 times during

each product life cycle.

Batteries fill landfills with toxic waste.

Energy harvesting wireless products counter the negative

impacts of wires and batteries since the resulting end

products do not require wiring or upkeep. Now that

OEMs can design past the limits of traditional power

sources, they can enter solutions into the marketplacethat make a compelling case for integrating impactful

interoperable building energy management systems

right now.

Using Energy at Its Source

EnOcean technology is rooted in the field of sensors

which offer numerous possibilities for making systems

smarter and more efficient. In buildings, for example,

sensors can measure important data from heating

or air-conditioning systems to help reduce energy

consumption. 20th century sensors are usually wired

or battery operated, requiring routine replacement and

regular maintenance.

EnOcean engineers solved the problem by using the

energy harvesting principle. Wherever there is motion,

light, heat or differences in temperature, there exist small

amounts of energy that can be harvested. Pressing a

button is enough to transmit a wireless signal and turn

on a light for instance.

Mechanical harvests energy from motion

Solar harvests from indoor light

Thermoelectric harvests from temperature differentials

Complete components for a system

The power for the wireless modules is produced by

energy converters, such as an electrodynamic energy

generator that makes use of mechanical motion, or a

miniaturized solar module. EnOcean modules use this

energy to detect information and transmit it wirelessly.

An additional charge capacitor can ensure an adequate

power reserve to bridge intervals when little or no energycan be harvested. Much like the power reserve of an

automatic clock, it stores energy for phases in which

there might not be enough light to operate an energy

harvesting module by a mini solar cell. In complete

darkness the energy stored will suffice for several days

of regular operation. EnOcean-enabled devices are also

able to work in difficult ambient conditions. Additionally,

modules save energy by executing all operations of

sensors and actuators very rapidly, and promptly turning

off when they are not needed. For this purpose the sensor

modules incorporate special timers that draw only about

20 nanoamperes of current, fully deactivating all other

components during sleep phases and waking them

again when they are required to operate.

Besides harvesting energy from light or motion, EnOcean

wireless modules can use heat as a power source.

Electricity is produced from differences in temperature,

from the heat of parts of machinery for instance, radiators

or even the human body. This means that radiator valves,

Figure 1: Sources available for powering building automation devices

Line Power Battery Power Energy Harvesting

solarmechanical thermoelectric



TECHNICAL ARTICLE

ventilation flaps or sensors can be deployed wherever

heat is available.

Radio signals use minimal energy

Wireless technology plays a special role in how theenergy harvesting modules work. The EnOcean

wireless signal is transmitted in the 868 MHz or 315 MHz

frequency band. Telegrams are just one millisecond

in duration. Although transmitted power is up to 10

milliwatts, the wireless transmission used here only has

an energy requirement of 50 microwatt seconds for a

single telegram. Requiring so little energy, a sensor can

be powered simply by operating a light switch to send

the necessary wireless signal to a lamp.

The short telegram is randomly repeated twice in the

space of about 40 milliseconds to prevent transmissionerrors. Transmitting data packets in random intervals

make the probability of collision extremely small.

Installation and parallel operation of a large number

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deviations or irregularities. The major advantage is

Figure 2: Primary types of energy harvesting wireless

modules



TECHNICAL ARTICLE

that the batteryless solutions can be flexibly located

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16/22



TECHNICAL ARTICLE

Using an FDA andInput Transformer

Michael SteffesIntersil - Sr. Applications Manager

ImprovedNoise Figure

Abstract: It is well known that combining a

transformer with various types of amplifiers

can improve the dynamic range. This works

particularly well driving into the inverting

side of either a differential dual op amp or

a Fully Differential Amplifiers (FDAs). This

approach has a number of subtle aspects

exploiting the source impedance referred

through the transformer to decrease theNoise Gain for those elements that get

to the output by this gain. Those features,

along with a detailed output noise analysis,

simulation confirmation, and the resulting

Noise Figure (NF) expressions, will be

described here.

Differential Inverting Circuit with a

Wideband Transformer Input

One of the lowest noise and distortion approaches to

moderate frequency (



TECHNICAL ARTICLE

they can be driven into the transformer differentially as

well.2. Since the 2 Rg resistors feed into a differential virtual

ground, they sum and input refer as a (2*Rg/n^2) input

impedance at the transformer. To get a midband match,

Rg is then completely constrained in this topology to be

Rs*(n^2)/2

3. DC operating point isolation. Many designs operate

single supply where the common mode control of an

FDA like the ISL55210 sets the Output common mode.

Here, since there is no DC path for a common mode

current to flow, the amplifier input pins will also be at the1.2V internal default common mode shown in Figure 1.

4. From the voltage delivered at Vi, the transformer steps

up the swing by the turns ratio and then that voltage gets

to the output by the Rf/Rg ratio(Av). In this circuit, set the

Rg resistors to get the match and then scale the gain to

Av by adjusting the Rf resistors.

5. More interesting is the gain to the output for the FDA

differential input noise. Since it sees both Rg and the

source impedance reflected through the transformer as

another Rg value on each side, that Noise Gain will be1+Rf/(2Rg) or 1+Av/2. This circuit has the remarkable

effect of giving more signal gain than Noise Gain when

Av > 1/(n-0.5). For any particular target gain from Vi to

Vo, this will normally improve the SNR.

All of this comes at the cost of higher resistor noise

and gain for the current noise terms at the input of the

amplifier. Using this approach also needs to consider

the bandwidth effects of the transformer, which limits

the range of turns ratios that might be applied. Table 1

shows some representative wideband transformers and

their useable frequency range. These are pretty forgiving

on the actual source and termination impedance. As

those change from the expected or characterization

values, the passband frequencies simply shift (ref.1).

As the turns ratio increases, it is easy to see in table 1 that

the useable flat bandwidth is compressing. As a practical

matter, turns ratios from 1:1.41 to 1:3 are readily available

for application to this approach. All of the devices in table

1 happen to offer a secondary centertap. Most of the

time, it is preferable to leave that floating (DC and AC)

in this application to avoid secondary imbalance issues

from getting into the signal path and/or giving a DC path

for the common mode current to flow.-1dB Frequencies

1.41

1.41

1.41

1.41

1.41

1.41

ADT2-1T

TX-2-5-1

WBC2-1TL

PWB-2-BL

CX2045NL

ADT3-6T

ADT4-1WT

ADT4-1T

ADT4-6T

WBC4-1TL

PWB-4-BL

MABA-009600

CX2047NL

ADT9-1T

WBC9-1T

T16-1H

WBC16-1TL

50

75

50

50

75

50

50

50

50

50

50

50

50

50

50

50

50

Yes

Yes

Yes

Yes

Yes

Yes

Yes

Yes

Yes

Yes

Yes

Yes

Yes

Yes

Yes

Yes

Yes

1

100

0.4

0.264

3

0.2

6

14

0.15

0.5

0.272

1

0.15

2

0.58

15

1.2

200

800

260

200

300

250

260

500

200

380

356

300

600

150

261

40

157

MiniCircuits

MiniCircuits

Coilcraft

Coilcraft

Pulse Eng

MiniCircuits

MiniCircuits

MiniCircuits

MiniCircuits

Coilcraft

Coilcraft

Macom

Pulse Eng

MiniCircuits

Coilcraft

MiniCircuits

Coilcraft

Turns Ratio Part Number Specified Ohms Centertap Fmin MHz Fmax MHz Manufacturer

Figure 1 is showing an example using a very broadband,

low noise device in this implementation. The Voltage

Feedback Amplifier (VFA) ISL55210 (ref. 2) provides

4GHz of gain bandwidth product with only 0.85nV/Hz

differential input noise and 5pA/Hz current noise on

each input. It does this using only 35mA on a single 3.3V

supply for 115mW power dissipation. The same basic

design, however, can also be implemented with any of awide range of Voltage Feedback Amplifiers (VFA) like the

1GHz ISL55190 as shown in Figure 2 (ref.3). This gives

a huge range of supply and speed options to this basic

circuit if the full universe of wideband VFA op amps can

be used. And of course this circuit is particularly suitable

to using duals.

Figure 2 is a simulation schematic implemented in a

free, locally running, Spice simulation tool (ref.4). It

Figure 1: Differential Inverting FDA Design with an InputTransformer

Table 1: Representative Wideband Transformers for Applicationin Figure 1



TECHNICAL ARTICLE

offers an easy means to generate the typical results for

both AC and output noise. In this example, a single 5V

operation is assumed with a DC bias midpoint applied

to the V inputs and the same basic signal path as an

FDA implementation. The output is sensed through

a dependent voltage source to convert differential to

single ended to plot the differential output noise. The

input transformer is a 1:2 turns ratio (RF transformers

are normally specified in ohms ratios, so the 4 in the

part number is the ohms ratio while the turns ratio is 4

= 2) terminated with the 2-100 gain resistors, then theamplifier signal gain is 6V/V giving it a total signal gain

of 12V/V. Using a VFA takes advantage of the reduced

Noise Gain. For the 1GHz Gain Bandwidth Product for

the ISL55190, this NG=4 should give an F-3dB of 250Mhz

in that stage while the WBC4-1TL should be relatively

flat. Figure 3 shows the simulated frequency response

while Figure 4 shows the output spot noise simulation.

This frequency response from the source in Figure 2, so

a 6dB loss from the expected gain of 21.6dB and the AC

coupling part of the response are shown in Figure 3. This

is showing 0.5dB flatness from about 600kHz to 120Mhz.

16

15

14

13

12

11

10

200k 400k 1M 20M 4M 10M 20M 40M 100M 200M 400M

Frequency / Hertz

db@V

OUT/dB

20n

10n

20k 40k 100k 200k 400k 1M 2M 4M 10M 20M 40M

Frequency / Hertz

Ou

tputNoise/V/rtHz

100M

Figure 4 shows a midband spot noise of 12.4nV with some

peaking towards 100Mhz associated with the response

shape of the ISL55190 inside this circuit. A noise gain of 4

is relatively low for this device so its response is actually

peaking, which shows up more in the noise plot than the

overall response plot. Input referred to the transformer

input at this gain of 12 gets this output noise very closeto 1nV at the input of the transformer including all terms.

Detailed noise calculations for the dual op

amp circuit

Each of the possible noise sources of Figure 2 can be

placed into this circuit and combined to the output. One

way to do this is to superimpose each voltage or current

noise source, find its gain to the differential output voltage,

then RSS those to get the combined output spot noise

Figure 2: Dual Op Amp Version of the Inverting Transformer Coupled Circuit.

Figure 3: AC Response for Figure 2

Figure 4: Output Differential Spot Noise for Figure 2



TECHNICAL ARTICLE

to compare to the midband number in Figure 4. Table 2

steps through the noise calculation for this example.

Here each noise term gets generated then its gain to the

output is used to get each terms spot noise contribution

at the output in V/Hz. Then, the noise power for each

term is formed, summed, and then the square root of

that is taken to estimate the combined spot noise at the

output of Figure 2.

Looking at each voltage or current noise term at the

bottom of this table

1. The Rs noise is divided by 2 to the input then gainedup so it gets to the output with a gain of 6

2. There are 2- Rg resistors, so the spot noise is 2 of a

single Rg noise it gets to the output by the noise gain

of 4.

3. There are 2-Rf resistors, so the spot noise is 2 of a

single Rf noise it gets to the output by gain of 1

4. There are 2 op amp Eni terms, so their combination is

2 of a single op amp it gets to the output by the noise

gain of 4

5. There are 2 inverting input current noise terms, so

they get a 2 multiplier as well and then get to the output

by the Rf resistor value.

Executing this calculation using the circuit values shown

predicts 12.5nV total differential output spot noise very

close to the 12.4nV simulation value.

Going to the FDA implementation of Figure 1 will change

this calculation slightly. First, there is only one differential

input noise voltage so it does not get the 2 multiplier of

the dual op amp design. More interesting is the current

noise. There is always the question of whether the two

current noise inputs might be correlated which changes

the 2 adjustment in the table to something closer to asimple 2 value. For dual op amps, the real number is

probably closer to 2 while for an FDA, where the inputs

really are the two sides of a single differential input

stage, something > 2 should be expected. Often, the

measured noise is just slightly over this uncorrelated

noise term model and that might be explained by this

effect.

Converting this output differential noise

to a Noise Figure

Having the full output differential noise expression,

including the contribution of the source noise from Rs, will

allow the Noise Figure expression to be derived. There

are many versions of the basic Noise Figure expression,

but the simplest for the purpose here is given in Eq. 1.

Total Differential Output Noise Calculations Dual Op Amp Implementation

Total Target Gain

Signal Gain =

Noise Gain

Rg value

Rf value

Rs value

Amplifier Eni

Amplifier In

Noise Source

Rs resistor noise

Rg resistor noise

Rf resistor noise

Eni noise

In noise

2

12

n*Rf/Rg

(1+Rf/(2*rG))

(n2)*Rs/2

Rg * Av

1.05E-09

5.50E-12

Noise expression

4kTRs

2*4kTRg

2*4kTRf

eni*2

in*2

Required Av

value

value

value

value

value

V/Hz

A/Hx

Source Value

8.94E-10

1.78885E-09

4.38178E-09

1.48E-09

7.78E-12

6

12

4

100

600

50

Gain

6

4

1

4

600

V/V

V/V

ohm

ohm

ohm

Output Value

5.337E-09

7.15542E-09

4.38178E-09

5.94E-09

4.67E-09

Output Power

2.88E-17

5.12E-17

1.92E-17

3.53E-17

2.18E-17

Total output spot noise power

Total output spot noise voltage

1.5626E-16

1.25004E-08

Target Turns Ratio

The 2 terms inside the log expression are simply forming

the ratio of the total output noise getting input referred

by the gain (and this is including the Rs noise) ratiold

against the noise delivered by the source resistance tothe input. These are always done in noise powers, so that

becomes noise voltages squared. Just dividing all the

terms making up the output noise power by (nAv)^2 will

generate the ei2 in Eq. 1. The kTRs is the noise power of

the Rs resistor delivered to a matched load. So that spot

noise voltage gets divided by 2 then squared to get the

power (which is why the 4 in the 4kTRs goes away).

Since all of the resistor terms in this design are

determined by the source impedance, turns ratio, and

then the target gain, the full Noise Figure expression will

actually drop all of those out leaving just gain dependentterms, the turns ratio, and the amplifier noise terms. The

full Noise Figure expression for the dual op amp design

of Figure 2 is given in Eq. 2 (where here a=Av=Rf/Rg)

Going to the FDA implementation simply drops the 2

from the voltage noise term to become Eq. 3

Table 2: Detailed Output Spot Noise Calculation

NF = 10Log(1 +e2i

kTRs)

NF= 10 Log(3 +8

+

4

2+

2 eni

1

2+ 1

2

+ 12 (n ibi Rs)

2

kTRs)



TECHNICAL ARTICLE

It is easy to see in these equations that increasing

the turns ratio (n) will decrease the amplifier voltage

Figure 5, will be giving about the same Noise Figure but

a noise gain of 4.6.

Summary and Conclusions

Teaming a broadband input step up transformer with adifferential inverting design can give an improvement in

input referred noise. Using a VFA in the design will also

be giving a lower noise gain than signal gain extending

the amplifier closed loop bandwidth and increasing

the loop gain. The dual op amp version can be applied

using any of a wide range of dual, high performance op

amps. The FDA version can actually give slightly lower

noise but will be constrained by the narrower range of

choices in implementation for this newer type of device.

Emerging high performance data acquisition platforms

make good use of this technique and FDAs to deliver

very high dynamic range solutions showing excellent

power efficiency (ref. 5).

References

1. Contact the author for a simple Spice Transformer

modeling technique.

2. ISL55210, 4GHz, 0.85nV, FDA. http://www.intersil.com/

content/intersil/en/products/amplifiers-and-buffers/all-

amplifiers/amplifiers/ISL55210.html

3.ISL55190, Dual 1Ghz, 1.05nV Op Amp. http://www.intersil.com/content/intersil/en/products/amplifiers-and-

buffers/all-amplifiers/amplifiers/ISL55190.html

4. iSim PE local simulation platform download

(registration required). http://intersil.transim.com/

iSimPE.aspx

5. Ultra Low Power 8 to 14bit data acquisition

platform. http://www.intersil.com/content/dam/Intersil/

documents/an17/an1725.pdf

About the Author

With 27 years of involvement in high speed amplifier

design, applications, and marketing, Michael Steffes has

introduced over 80 products spanning five companies

while publishing more than 40 technical articles. His

current focus is on high efficiency high speed ADC

interfaces, DSL/PLC line interface solutions, and online

design tool development.

noise contribution while increasing the current noise

contribution. Increasing the amplifier gain will decrease

the Noise Figure monotonically. It is typical to solve for

an optimum n for these equations. However, turns

ratios are most easily available in specific steps as

shown in Table 1. It might be more interesting to pick 4

different turns ratios and then sweep the amplifier gain

achieving the same overall gain range in the analysis. For

higher turns ratios, this means the amplifier gain span

will be shifting down. That will be acting in the directionof increasing the Noise Figure, but will be giving wider

bandwidth for any given amplifier. Continuing the

ISL55190 example and generating the NF from Eq. 2

sweeping total gain from 4V/V to 40V/V (12dB to 32dB)

gives the plot of Figure 5.

12

11.5

11

10.5

10

9.5

9

8.5

8

7.5

7

n=1.41

n=1.73

n=2

n=3

12

Gain in dB

NF vs Gain (ISL55190)

Noise

Figu

re

(dB)

17 22 27 32

Surprisingly, the net result of Eq. 2 gives about the same

profile of noise figure vs. gain until the turns ratio gets

to 3. This suggests that using the highest turns ratio

consistent with the desired signal band and allowing the

amplifier gain to go down might actually be desirable.Operating with lower amplifier gain will also improve the

loop gain for VFA based designs, possibly improving the

harmonic distortion performance as well. For example,

to get a 20dB gain, figure 5 would suggest using a turns

ratio of 2 and an amplifier gain of 5 where the Noise Figure

should be about 8.4dB. This Av = 5 will be a noise gain

of 3.5 giving a bit more loop gain than say using a n=1.41

and then an amplifier gain of 7.1, which, according to

Figure 5: Swept Gain Noise Figures with 4 Steps of Turns Ratios

NF= 10 Log(3 +8

+

4

2+

2 eni

1

2+ 1

2

+ 12 (n ibi Rs)

2

kTRs)
http://www.intersil.com/content/intersil/en/products/amplifiers-and-buffers/all-amplifiers/amplifiers/ISL55210.html%3C2028%3Ehttp://www.intersil.com/content/intersil/en/products/amplifiers-and-buffers/all-amplifiers/amplifiers/ISL55210.html%3C2028%3Ehttp://www.intersil.com/content/intersil/en/products/amplifiers-and-buffers/all-amplifiers/amplifiers/ISL55210.html%3C2028%3Ehttp://www.intersil.com/content/intersil/en/products/amplifiers-and-buffers/all-amplifiers/amplifiers/ISL55190.html%20%3Chttp://www.intersil.com/content/intersil/en/products/amplifiers-and-buffers/all-amplifiers/amplifiers/ISL55190.html%3Ehttp://www.intersil.com/content/intersil/en/products/amplifiers-and-buffers/all-amplifiers/amplifiers/ISL55190.html%20%3Chttp://www.intersil.com/content/intersil/en/products/amplifiers-and-buffers/all-amplifiers/amplifiers/ISL55190.html%3Ehttp://www.intersil.com/content/intersil/en/products/amplifiers-and-buffers/all-amplifiers/amplifiers/ISL55190.html%20%3Chttp://www.intersil.com/content/intersil/en/products/amplifiers-and-buffers/all-amplifiers/amplifiers/ISL55190.html%3Ehttp://intersil.transim.com/iSimPE.aspx%3Chttp://intersil.transim.com/iSimPE.aspx%3Ehttp://intersil.transim.com/iSimPE.aspx%3Chttp://intersil.transim.com/iSimPE.aspx%3Ehttp://www.intersil.com/content/dam/Intersil/documents/an17/an1725.pdfhttp://www.intersil.com/content/dam/Intersil/documents/an17/an1725.pdfhttp://www.intersil.com/content/dam/Intersil/documents/an17/an1725.pdfhttp://www.intersil.com/content/dam/Intersil/documents/an17/an1725.pdfhttp://intersil.transim.com/iSimPE.aspx%3Chttp://intersil.transim.com/iSimPE.aspx%3Ehttp://intersil.transim.com/iSimPE.aspx%3Chttp://intersil.transim.com/iSimPE.aspx%3Ehttp://www.intersil.com/content/intersil/en/products/amplifiers-and-buffers/all-amplifiers/amplifiers/ISL55190.html%20%3Chttp://www.intersil.com/content/intersil/en/products/amplifiers-and-buffers/all-amplifiers/amplifiers/ISL55190.html%3Ehttp://www.intersil.com/content/intersil/en/products/amplifiers-and-buffers/all-amplifiers/amplifiers/ISL55190.html%20%3Chttp://www.intersil.com/content/intersil/en/products/amplifiers-and-buffers/all-amplifiers/amplifiers/ISL55190.html%3Ehttp://www.intersil.com/content/intersil/en/products/amplifiers-and-buffers/all-amplifiers/amplifiers/ISL55190.html%20%3Chttp://www.intersil.com/content/intersil/en/products/amplifiers-and-buffers/all-amplifiers/amplifiers/ISL55190.html%3Ehttp://www.intersil.com/content/intersil/en/products/amplifiers-and-buffers/all-amplifiers/amplifiers/ISL55210.html%3C2028%3Ehttp://www.intersil.com/content/intersil/en/products/amplifiers-and-buffers/all-amplifiers/amplifiers/ISL55210.html%3C2028%3Ehttp://www.intersil.com/content/intersil/en/products/amplifiers-and-buffers/all-amplifiers/amplifiers/ISL55210.html%3C2028%3E


22/22

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